1. Field of the Invention
This invention relates to a ΣΔ (sigma-delta) analog-to-digital converter including a ΣΔ modulation section for executing ΣΔ modulation and a digital filter for filtering a digital signal output from the ΣΔ modulation section, and in particular relates to a ΣΔ analog-to-digital converter having improved noise immunity.
2. Description of the Related Art
A ΣΔ analog-to-digital converter including a ΣΔ modulation section for executing ΣΔ modulation and a digital filter for filtering a digital signal output from the ΣΔ modulation section is known.
JP-A-2004-247930 and JP-A-5-37385 are referred to as related art.
According to an environment where a ΣΔ analog-to-digital converter is used, noise whose frequency is fixed may be mixed into an analog input signal. For example, noise of a commercial frequency (hereinafter, commercial frequency) may be superposed on an input signal, thereby adversely affecting the operation of the system using the ΣΔ analog-to-digital converter.